Spherical Diamond Phylactery

In a game I am running, a now-lich used a form of magic that permanently reshapes matter to create a spherical diamond to use for his phylactery, since normal diamonds can be damaged moderately easily if you hit them at an edge. I’m imagining the crystal lattice being sort of bent, though I’m open to alternative explanations as long as it leaves the result being properly spherical instead of just having a lot of faces. The players are going to find the phylactery soon and try to destroy it.

Roughly how much force would it take to damage a diamond like that? Do I need to include metal wires reinforcing it? Would that even help protect it from impact damage?

I’m running using Gumshoe in a modern setting, though the phylactery was created in Roman times.